Automotive alternators are known to be mounted on gasoline or diesel engines in the engine compartment of the vehicle. The engine compartment has been and remains a hot environment. The heat from the radiator is carried into the engine compartment and baths the engine, alternator and components mounted in the engine compartment. Additionally, heat radiated or conducted from the engine block also baths the alternator and other components in the engine compartment.
While the vehicle is moving, ventilating air generally flows from the front of the vehicle, through the radiator, across the engine and down underneath the vehicle. When the vehicle is standing, however, the airflow becomes minimal through the engine compartment, and much of the heat rises to the upper portion of the engine compartment, in which the alternator typically is located.
The alternator does not depend on the fan pulling air through the radiator for its cooling, but upon its own fan for drawing ventilating air through it. The fan pulls air in through perforations in the rear wall of the alternator, across the regulator and diode assembly heat sinks, between the stator and rotor assemblies and out openings in the front wall of the alternator. The alternator fan thus works against the air being drawn through the radiator and into the engine compartment. In addition to the heat generated by the engine, the alternator also produces substantial quantities of localized heat in producing the 50 to 80 amperes of electrical current often demanded in automotive vehicles. Temperatures of components inside the alternator often can reach 450-500.degree. F. in these circumstances. These temperatures often approach the specified limits of components, such as the rectifier diodes, and power transistor in the rectifier.
This hot environment, which gives rise to the invention, becomes accentuated when the vehicle is standing and the engine is idling. The fan on the alternator often is inefficient in pulling air through the alternator, especially at low speeds. Further, as any motorist knows, an idling engine in a standing vehicle is poorly cooled and often rapidly increases in temperature. This regularly results in the overheating of engines on a hot summer afternoon in stop-and-go city traffic. While this heat is hard on engines, it is harder on alternators. The poor ventilation provided by the alternator fan or impeller moving air from the rear to the front of the alternator must fight the engine ventilating air moving from the front to the rear of the engine compartment. As a result, the small amount of ventilating air entering the idling alternator tends to stagnate in the rear chamber of the alternator between the rear wall, the rotor and stator laminations and the circumferential wall of the alternator housing. With poor ventilation, heat produced by the alternator tends to collect in the rear chamber, and if the alternator does not have proper thermal protection, the temperature at the rectifier diode junctions can exceed their ratings and be destroyed. This heat also has deleterious effects on the components in the regulator.
While the components of the alternator can be made more rugged to withstand the high temperatures experienced in an automotive alternator when the vehicle is standing and the engine is idling, such undesirably increases the cost and size of the automotive alternator.
What is desired is an automotive alternator that can withstand such harsh temperatures for extended periods while producing high current output. Such an alternator should have little increased cost or size to achieve the desired qualities. Further, it would be advantageous if an automotive alternator could produce substantially increased current with substantially no increase in cost or size and no decrease in expected life.